The present invention relates to projection cathode ray tubes, and more particularly, to an improved mounting for the target assembly of the tube to prevent defocusing of the image due to inadvertent shock loading.
The use of projection cathode ray tubes to project electronically generated images onto viewing screens is well known in the art. These tubes are utilized in various display environments, such as in flight simulators for training aircraft pilots. An electron beam generates an image on a sensitive coating of the target of the tube and by projection through a Schmidt optical projection system the image appears on a screen, such as in the flight simulator in front of the pilots to simulate the view from a cockpit of the aircraft. In such an arrangement, it is critical to maintain a sharp image in order to satisfy the overall objective of creating as close to a live training environment as possible. A sharp image of the simulated view from the cockpit enhances the pilot's performance thus improving the efficiency of the practice or testing session for the pilot.
Thus, substantial research and development has been directed to improving the focus of the projection tube. Improvements in the quality of the glass tube, the Schmidt optical projection system, the surface of the target member and the electron gun are included. In addition, efforts have been made to improve the structure of the target assembly, including the mounting arrangement for the target and the heat dissipating structure. The standard of the industry in this respect is shown in U.S. Pat. No. 4,177,400 to Hergenrother et al., issued Dec. 4, 1979. The target assembly is mounted on the internal face plate of the projection tube and held in position by a compression spring on one side and a tripod mounting pad on the other. Final tilt adjustment of the target member is provided by three set screws on the pad. The compression spring is designed to hold the center shaft screw in tension and maintain the target in the proper spatial relationship within the tube, and thus to secure the focus of the image of the tube.
While this prior art arrangement shown in the '400 patent has been successful, the projection tubes including this target assembly require extreme handling procedures. The problem is that after the focus is set by adjusting the set screws on the adjustment pad, this tube of the prior art can sometimes be knocked out of focus inadvertently by a relatively mild bump or jar. Such inadvertent shock loading can occur in any number of ways during the final stages of manufacturing, transporting to the OEM manufacturer, during actual installation and during subsequent use and servicing. Thus, it would be desirable to provide an improved target assembly that protects the target member from displacement and the tendency to tilt, and thus minimize the tendency to defocus the tube. Such support structure should be able to be economically manufactured, while at the same time holding the target member more rigidly. Also, it would be a plus to provide an arrangement allowing easier servicing and refocusing during the life of the tube in the unlikely event that it is required.